Laser materials processing as known in the art and used herein refers to performance of materials processes, such as cutting, welding, drilling and soldering, using a continuous wave or pulsed laser beam. The average power of such a laser beam may range from as little as approximately one watt to 100's of watts, the specific power being selected on the basis of the particular process being performed. Laser beam power required for materials processing generally is much greater than laser beam power required for other laser-based systems such as communication systems.
At an early stage of laser technology advancements, a laser beam emitted directly from a laser source was utilized for laser materials processing. The mobility of such laser systems was limited and it was difficult to effectively incorporate such systems into a manufacturing environment. The laser source and optical components had to be located close to process points on a workpiece.
Transmission of laser beams through optical fibers, at power levels suitable for performing materials processing, greatly enhanced the flexibility of laser-based materials processing systems. The transmission of high power beams through an optical fiber, however, presented difficulties not encountered in low power beam optical fiber transmission. For example, beam injection techniques utilized for injecting low power beams, such as beams used in communication systems, into an optical fiber generally are not suitable for high power beam injection. In fact, utilizing a low power beam injection technique for injecting a high power beam may result in damaging the optical fiber. Various techniques for the efficient injection of a high power laser beam into an optical fiber for transmission therethrough are disclosed, for example, in commonly assigned U.S. Pat. Nos. 4,564,736; 4,676,586; and 4,681,396 respectively entitled "Industrial Hand Held Laser Tool and Laser System", "Apparatus and Method for Performing Laser Material Processing Through a Fiber Optic", and "High Power Laser Energy Delivery System".
High power beam transmission through optical fibers has obviated a need for positioning, close to a workpiece, a laser source and optical components otherwise required for directing a laser beam emitted from the source to process points on the workpiece. With optical fiber high power laser beam transmission, an output end of each optical fiber is disposed in an output coupling device which includes means to collimate and focus the beam emitted from the fiber output end. The output coupling device is easily moved relative to a workpiece by, for example, a computer-controlled robotic arm. The number of fibers and their respective output ends proximate process points on a workpiece may vary.
Monitoring materials processing when utilizing optical fiber based systems is much more difficult than monitoring processing when a beam emitted from the laser source is directly utilized for processing. Specifically, with optical fiber transmission, a system user must monitor, during the processing and in addition to the laser source, a beam injection system, an output coupler, and an optical fiber. Failure of any one component may result in failure of the entire system.
Also available to enhance laser materials processing are systems for time sharing of a materials processing laser beam among a plurality of optical fibers. Such systems are described in commonly assigned U.S. Pat. Nos. 4,739,162 and 4,838,631 entitled "Laser Beam Injecting System" and "Laser Directing System", respectively. Manufacturers of beam time sharing systems include Robolase Systems, Inc. of Costa Mesa, Calif. and Lumonics Corporation of Livonia, Mich. By the use of such beam time sharing systems, a beam generated by one laser source can be shared among multiple optical fibers. The respective output ends of each optical fiber may be positioned proximate respective process points on one or more workpieces.
Laser beam time sharing systems, sometimes referred to as multiplexers, have further increased the flexibility and efficiency of laser materials processing. The control and monitoring of such multiplexer-based systems not only has increased importance but also has increased difficulty. The system user must monitor a laser source, a multiplexer, multiple beam injecting systems, multiple couplers, and multiple optical fibers.
As laser materials processing has progressed from using, directly, a beam emitted from a source to using multiple beams emitted from multiple fibers, more sophisticated control and monitoring of the process have become needed. The control and monitoring systems preferably facilitate obtaining desired processing results and aid in preventing damage to the processing equipment. The control and monitoring systems, however, should not slow down the laser materials processing operations. Otherwise, advantages of utilizing optical fiber/laser technology, such as a reduction in processing time, may be lost.
Further, it is preferred that control and monitoring systems operate in substantially real-time. As used herein, the term "real-time" means the actual time which each discrete process operation is performed. For example, a discrete process operation may be drilling one hole. It is most desirable that a control and monitoring system be able to obtain data simultaneous with and during each discrete operation so that if adjustments to processing equipment are needed, such adjustments can be made before a next hole is drilled, i.e., before a next process operation. It should be understood that the time required to perform a discrete process operation may be short, such as a few micro-seconds. The control and monitoring system, therefore, must perform its functions very quickly.
An entire process operation, of course, generally includes many discrete process operations. Consider, for example, laser drilling of an aircraft engine combustor and afterburner parts. These parts are made from high temperature steel alloys and require tens of thousands of 0.020 inch (0.0508 cm) holes drilled at 20 degrees to the surface, where wall thickness may vary from 0.020 inch (0.0508 cm) to 0.080 inch (0.2032 cm). In order to timely complete the entire process operation, monitoring and controlling the formation of each hole should be performed quickly.
A known method for monitoring laser drilling operations is referred to as air flow testing. For an airflow test, a workpiece such as an aircraft engine combustor part is removed from the drilling apparatus and a known pressure differential is applied across the workpiece. The resulting air flow is measured to provide a measure of flow resistance. Flow resistance is related to a measure of drilled area, i.e., the diameter and shape of the drilled holes. Air flow testing, however, is not a real-time operation in the sense that laser processing cannot take place on a workpiece during an air flow test. An air flow test limitation is that it also is not an indicator of other hole geometric properties, e.g. recast layer thickness, hole taper, etc.
Another known method for checking the results of a laser drilling operation is "pin checking". In a pin checking operation, drilling is stopped, and then pins of successively increasing diameter are successively inserted into selected holes. Pin checking provides an approximate indication of hole diameter because laser-drilled holes are rarely perfectly straight, thus blocking insertion of the pins. Pin checking also is not a reliable indicator of other hole geometric properties nor is it a real time process. Further, only selected holes are analyzed in the pin checking procedure and differences between each hole may not be detected.
It is therefore an object of the present invention to provide a method and system for detecting and monitoring, in substantially real time, laser materials processing.
Another object of the present invention is to provide a method and system for detecting and monitoring laser materials processing which do not slow down the processing operations.
Still another object of the present invention is to provide a method and system for detecting and monitoring laser materials processing which allow continuous monitoring of the processing operations and provide an indication of geometric properties including recast layer thickness and hole taper.
Still yet another object of the present invention is to provide a method and system for detecting and monitoring laser materials processing which operate simultaneously with the processing operations.
Another object of the present invention is to provide a method and system which utilize optical sensors to monitor plasma generated during a laser materials processing operation, and from data provided by the sensors, control the processing operations.
Still another object of the present invention is to provide a control system which facilitates obtaining consistent laser materials processing performance.
Still yet another object of the present invention is to provide a method and system for monitoring and controlling performance of laser materials processing components.